Small precise control motor is generally divided into AC motor, DC motor, BLDC (Brushless) motor and Reluctance motor.
Recently, small motor becomes key component for development and competitiveness of relevant products as driving source and control source of several electronic apparatuses and precise apparatuses because the kind of control apparatuses along with high quality of vehicles increases. Accordingly, driving motor is required to be smaller and less noisy and to consume less power, etc.
BLDC motor has no brush and commutator, so it does not make mechanical friction damage, spark and noise and its velocity control or torque control is remarkable. Also, there is no damage from velocity control and its efficiency as a small motor is excellent.
Besides, since the BLDC motor has advantages such as easy miniaturization, high durability, and long life without requiring maintenance, it is increasingly required for electronics.
FIG. 1 is control block view of control apparatus of conventional BLDC motor.
The control apparatus of conventional BLDC motor (10) comprises inverter (70), position detector (20), and PWM processor (50), and the inverter (70) converts DC voltage applied by bridge diode (not described in the FIG. 1) into AC voltage.
When the AC voltage is applied to the BLDC motor (10), the rotor of the BLDC motor (10) is rotated, and along with rotation of the rotor, position of rotor is detected by the position detector (20), and then control signal is output to driving signal generator (30) and velocity controller (40).
Velocity controller (40) determines rotation velocity of the BLDC motor by using information on position of the rotor provided by position detector (20).
Driving signal generator (30) makes driving signal for on/off switching operation of each transistor consisting of the inverter (70) and the driving signal is output to PWM processor (50). PWM processor (50) modulate (i.e. pulse width modulation) the driving signal input from driving signal generator (30) along with information on the rotation velocity input from velocity controller (40) to output it to gate driver (60).
Gate driver (60) provides the modulated driving signal to each transistor consisting of the inverter (70), and each transistor performs on/off switching operation to provide AC voltage to each phase (A, B, C) of each stator consisting of the BLDC motor (10). As a result, the rotor of the BLDC motor (10) rotates.
To drive the BLDC motor smoothly, position of the rotor should be precisely matched with conversion point of phase current.
That is why, when driving initially the BLDC motor, when changing its mode, or when driving the BLDC motor again after stopping the BLDC motor, forced driving method is chosen to amend initial position of the rotor of the BLDC motor. In other words, since repeatedly the rotor of the BLDC motor is compulsively aligned, start-up time of the BLDC motor becomes delayed.
According to Korean Patent No. 10-0327862 (Initial position detection and starting algorithm of BLDC motor using inductance variation), initial driving algorism is disclosed in which the BLDC motor detects position of rotation in stop state by pulse train acquired from change of inductance without additional sensor and performs initial driving smoothly.